Metal alloy foils, particularly of superalloys and other high melting point alloys, are of commercial interest for use in many applications, including the manufacture of metal matrix composites. Other potential applications of metal alloy foils, including foils of lower melting point alloys such as Al--Si alloys, may comprise use as cladding or coating materials to impart specific properties, such as corrosion, wear or oxidation resistance to a particular substrate.
However, the lack of low and/or high temperature ductility of many classes of alloys (or compositional ranges within certain classes of alloys), such as high melting point Ti-base, Ni-base, and Nb-base alloys and lower melting point alloys such as Al--Si alloys, have prevented, or at least limited, the development of metal alloy foils from these alloys. Often this lack of ductility is attributable to the existence of brittle phases, such as intermetallic compounds. These phases may result from segregation in bulk forms, in which case these phases would be absent if the bulk forms were fully homogeneous. This characteristic often limits, or rules out altogether, the use of related art foil-making methods that rely on cold-rolling techniques; since such alloys may not be readily rolled from their bulk forms, such as ingot, slab or sheet forms.
As discussed in the above-referenced patent applications and known generally by those of ordinary skill, related art metal alloys that can be made in foil form are further limited by one or more of the following characteristics: higher than desired concentrations of oxygen and/or nitrogen contaminants, grain orientation or elongation (e.g. grain elongation in a preferred direction) related to existing foil forming methods, and large grains which are either inherent to the starting material used to produce a foil or caused by grain growth related to existing foil forming processes.
Another known limitation of some related art metal alloy foils is that when available, they are costly. This is due in part to bulk material costs, as well as the fact that present methods of making such foils involve costly, complex, multi-step processes which combine various combinations of hot-working, cold-working, annealing and surface finishing, and often may involve substantial loss of the starting materials (e.g. chemical milling to produce Ti-base alloy foils). Also, whether due to cost or other considerations, relatively few high strength metal alloy compositions have been produced in foil form.